[aprssig] Barometric pressure compensation

Scott Miller scott at opentrac.org
Mon Oct 19 17:38:20 EDT 2009

I'm making good progress on my APRS weather station kit, but I've run 
into a minor snag.

To be useful, the station barometric pressure reading has to be reduced 
to sea level.  This means making an estimate based on a fictitious layer 
of air between the station and sea level, and that estimate makes 
assumptions about the temperature and lapse rate in that layer.

The NWS has an official algorithm for this, but it'd be rather tricky to 
implement in a low-cost station.  The other amateur stations I can find 
information on (uWeather, Hobby Boards) seem to have simple offsets with 
no temperature compensation, which seems a little too simplistic.

Among professional stations like those by Davis and Peet Bros, is there 
any standard for how the sea level reduction is calculated?  Or do we 
just assume that we're not going to get any meaningful data about 
horizontal pressure gradients from home stations and only look at one 
station at a time?


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